Sodium phosphate-citric acid-edta cleaning solutions for scaled ferrous metals



may

SODIUM PHOSPHATE-CITRIC ACID-EDTA CLEAN- ING SOLUTIONS FOR SCALED FERROUS METALS Cornel Wohlberg, Hempfield Township, Westmoreland County, Pa., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Filed Dec. 5, 1966, Ser. No. 599,675

Int. Cl. C02b 5/00; C23g 1/00; C09k 3/00 US. Cl. 252-87 1 Claim United States Patent 0 ABSTRACT OF THE DISCLOSURE A buffered mixture of sodium phosphate-citric-amino acids of the EDTA type is used to remove scale or deposited oxides from ferrous metals with a minimum of attack on the metal itself.

The inven'ion described herein was made in the course of, or under, Contract W-7405-ENG-36 wi.h the US. Atomic Energy Commission.

There is a need for an effective hot or cold cleaning agent for ferrous oxides and magnetite scale or deposit with a minimum of attack on the ferrous metals of the nons ainless types. Some of the characferistics of such a cleaning soluion should be 1) a good complexer in that at relatively high pH (approximately 7.0) no precipitate is formed, (2) able to dissolve oxide scale off an alloy steel pipe Crl% Mo), and (3) that little hydrogen is evolved. It is important therefore that the solution dissolves oxides rather than metals, and furthermore it is important to minimize the hydrogen evolved in order to avoid possibilities of hydrogen embrittlement. To this inventors knowledge, none of the above characteristics are combined in any presently known cleaning solution although there are many scaling or cleaning solutions for ferrous metals that have some of the above characteristics.

With the above characteristics in mind, the invenor has discovered that the following materials were suitable for formulating a cleaning solution for scaled ferrous metals: (1) citric acid, (2) phosphates, and (3) an EDTA type (ethylene diamine tetracetic acid). The citric acid acts as an excellent chelating agent over a wide pH range althrough its solvent ability diminishes with increasing pH while the phosphates as a group make excellent buffer sysfems. The EDTA is a second type of chelator and has a synergistic affect on the chelating and solvent effect of the citric acid.

It is therefore an object of this invention to provide a composition that is effective as a cold or hot cleaning agent for various ferrous oxides and magnetite scale or deposit with a minimum of attack on the metal itself.

Other objects of this invention will become apparent from the following description of the composition of the preferred embodiment.

g. of citric acid 10 N33P04 H Patented Jan. 27, 1970 ice 10 g. Versene Fe-3 sodium dihydroxyethylglycyine flake with a structural formula as follows:

( omen: o

NCHz-(l-ONa no CHrCHi ml. water.

The pH is maintained between 6.0 and 7.0.

Mixtures of citric acid and sodium phosphate in. the same pH range are not noticeably effective on scaled steel; however, other compounds such as the polyphosphates, gluconic acid, and EDTA may be used in various proportions as slated in the above formulation. In particular, the scaling solution is composed of a mixture of hydroxyacid, phosphate, and amino acid salt with said solution being maintained at a highspH (6.0-7.0);0 as to minimize hydrogen evolution and possible embfittlement of the alloy being cleaned.

The above scaling solution is a very effective cold or hot cleaning agent for ferrous oxides and magnetite scale, and in addition, there is a minimum of attack on the ferrous metal. Further characteristics of this cleaning solution are that little hydrogen is evolved, thus avoiding hydrogen embrittlement of the metal, and no precipitate is formed. Thus, only the oxide of the metal and not the metal itself is attacked by the solution.

What is claimed is:

1. A cleaningsolution for scaled ferrous metals and consisting of the following formula in equal parts by weight: citric acid; Na PO -12 H O; sodium dihydroxyethylglycine flake with a structural formula as follows:

(HCDCHQCH! Nom- ONa with sufficient water to maintain the pH between 6.0 and 7.0.

References Cited UNITED STATES PATENTS 2,396,938 3/1946 Bersworth 252-142 2,783,200 2/1957 Crum et al 25282 2,890,175 1/l'959 Kipps 252-87 2,994,664 8/1961 Wachter 252-87 3,003,898 10/1961 Reich 252-82 3,003,899 10/1961 Eberhard et a1. 252-142 3,013,909 12/1961 Pancer et al 134-3 3,063,944 11/1962 Zussman et al. 252-142 3,242,093 3/1966 Compton 252-142 3,397,149 8/1968 Gruber 252-82 MAYER WEINBLATT, Primary Examiner I. GLUCK, Assistant Examiner US. Cl. X.R. 

